Current computer systems typically include a graphic user interface that can be navigated by a cursor, i.e., a graphic element displayed on the screen and movable relative to other screen content, and which serves to indicate a position on the screen. The cursor is usually controlled by the user via a computer mouse or touch pad. In some systems, the screen itself doubles as an input device, allowing the user to select and manipulate graphic user interface components by touching the screen where they are located. While touch may be convenient and relatively intuitive for many users, touch is not that accurate. Fingers are fat. The user's fingers can easily cover multiple links on a crowded display leading to erroneous selection. Touch is also unforgiving—it requires the user's motions to be confined to specific areas of space. For example, move one's hand merely one key-width to the right or left and type. Nonsense appears on the screen.
Mice, touch pads, and touch screens can be cumbersome and inconvenient to use. Touch pads and touch screens require the user to be in close physical proximity to the pad (which is often integrated into a keyboard) or screen so as to be able to reach them, which significantly restricts users' range of motion while providing input to the system. Touch is, moreover, not always reliably detected, sometimes necessitating repeated motions across the pad or screen to effect the input. Mice facilitate user input at some distance from the computer and screen (determined by the length of the connection cable or the range of the wireless connection between computer and mouse), but require a flat surface with suitable surface properties, or even a special mouse pad, to function properly. Furthermore, prolonged use of a mouse, in particular if it is positioned sub-optimally relative to the user, can result in discomfort or even pain.
Accordingly, alternative input mechanisms that provide users with the advantages of intuitive controls but free the user from the many disadvantages of touch based control are highly desirable.